1. Field of the Invention
The present invention relates to improved agents and products containing a calcium phosphate compound. More particularly, the present invention relates to a deodorant which can adsorb and remove different odor components. The present invention also relates to a functional sheet, especially a deodorant sheet containing the above deodorant, and a filter sheet which selectively traps a biological polymeric substance, bacterium, virus, animal or vegetable cell, toxic gas, odor component, dust or mist in a gas or liquid, but allows a permeation of other components. The present invention also relates to a functional paper used in different fields of technology, and is especially used as a deodorant, filtering medium and adsorbent. Also, the present invention relates to a filtering medium and filter cartridge for an exhaust gas as well as an exhaust gas filter. The filtering medium, filter cartridge and exhaust gas filter are disposed in an exhaust system to purify an exhaust gas. They can effectively trap soot or carbon dusts and also adsorb gaseous substances such as carbon monoxide or hydrocarbons, without causing a blocking of the pores of the filtering medium.
2. Description of Related Art
Hitherto, to remove any odor components or substances from the surrounding atmosphere or the like, many odor removing processes have been widely used, and typical examples of the well-known deodorizing processes include (1) the use of an aromatizing agent or fragrance to mask the odor, (2) the use of a catalyst to chemically decompose odor components to thereby make them odorless, and (3) the use of an adsorbent capable of adsorbing and removing any odor components. However, each of these three processes has problems to be solved.
For example, the aromatizing agent can sometimes emit an unpleasant smell to a person, because generally it must be an agent capable of emitting a strong fragrance in comparison with the odor components. The catalytic decomposition of the odor components is limited to only some of the odor components, because there is no known catalyst which is effective for all odor components. In addition, activated carbon, which is a typical example of well-known adsorbent-type deodorant, cannot effectively adsorb basic gases such as ammonia gas, although it can adsorb substantially all other odor components. Further, activated carbon must be used under conditions of low temperature, because it can be easily removed at an elevated temperature as a result of combustion. It is therefore desirable to provide an improved deodorant which is effective for all types of odor components and does not restrict the conditions of the usable working temperature.
In connection with the above-described adsorbents as a deodorant, it should be noted that hitherto, a fibrous substance such as filter paper or filter cloth, granular substance such as activated carbon, clay, gravel or diatomaceous earth, or porous substance such as porous pottery have been used as a filtering medium. Apparently, almost all of these filtering mediums are used to trap solid substances, and suitable filtering mediums are selected depending on the specific solid substances to be trapped or filtrated. However, the prior art filtering mediums suffer from some drawbacks.
Activated carbon has frequently been used as a filtering medium, because it exhibits an excellent adsorptivity. However, since it has no adsorption power for any oil-soluble substances or any malodorous components such as ammonia, activated carbon cannot be used to remove these substances and components from any gas or liquid containing the same.
Recently, a membrane filtering system has been developed, but it suffers from a high production cost, because it is essential to use an ultrafiltration membrane or reverse osmosis membrane. On the other hand, a bacterial filter such as a Seitz Filter has also been developed. However, the use of this filter is limited to the trapping of bacteria, and if used, the filtration must be carried out under conditions of reduced pressure or centrifugal force. As one will appreciate from the above, the prior art filtering mediums can only be applied to a limited range of substances to be filtered off, or require expensive filtering equipment.
Turning the discussion of the prior art to functional paper, as is well-known in the art, in the production of conventional white-colored papers, a filler is used to improve the opacity, smoothness, ease of writing, ink-receptivity and other properties of the papers. Typical examples of such filler include clay, talc, titanium white, calcium carbonate and the like.
Further, it is also well-known to produce ceramic paper from a pulp, skeleton material and fixing material, in accordance with paper production technology. However, the prior art methods are not suitable for the production of ceramic papers having a high flexibility equivalent to that of plain papers.
Furthermore, Japanese Unexamined Patent Publication (Kokai) No. 59-95931 teaches the production of papers having special functions in accordance with the specified method. The papers produced in accordance with this method contain finely divided particles of crystalline aluminum orthophosphate, and are characterized by their good capability of adsorbing odor components or substances. These functional papers can effectively adsorb odor substances such as ammonia, but cannot adsorb other odor substances.
Moreover, recently, developments and research for an exhaust gas filter, and a filtering medium and filter, cartridge for the filter have been extensively carried out to prevent air pollution.
Exhaust gases from an internal combustion engine or the like, for example, those from automobiles, contain nitrogen oxides NO.sub.x, soot or carbon dusts, carbon monoxide CO, hydrocarbons, and other gaseous substances. Since these substances cause air pollution, the discharge of such exhaust gases into the atmosphere is now controlled by air pollution control regulations or similar acts. The current regulations are generally directed to control of the nitrogen oxides only. However, as a recent development, the regulations have been expanded to also cover the control of soot dusts, carbon oxide and hydrocarbons discharged from diesel engines.
Previously, to remove fine dusts such as soot dusts from the exhaust gas discharged from a diesel engine, it has been conventional to pass the exhaust gas through a porous filter, such as cordierite, or a fibrous filter, such as quartz glass fibers or metallic fibers. The dusts are physically trapped by this porous or fibrous filter, and then heated to cause combustion thereof. However, the porous or fibrous filter has a drawback in that back pressure can increase due to the frequent blocking of the pores of the filter. It is also conventional to use a porous filter with a plurality of open pores in which each gas passage has a coating of an oxidation catalyst applied thereon. However, due to the complicated production process thereof, porous filters suffer-from a high production cost and a low dust trapping efficiency.